Realism or Nominalism: A Metaphysical Debate

Ever since the philosophers of ancient Greece there has been an ongoing debate about metaphysics, a debate that has moved through into the medieval era and even into modernity. The nature of this debate is whether the philosophic school of metaphysical realism; as upheld by Plato; or the philosophic school of nominalism; as upheld by Aristotle; shows us the true nature of reality.  On the one hand we have the belief that reality consist of things ordered by their abstract counterparts whilst on the other side of the debate it is believed that reality only consists of concrete things and to talk of such abstract ideas is an absurdity. The answer to this debate is elusive but via studious contemplation it becomes apparent that truth lies with the realists in that reality is governed by a set of abstract entities known as universals. Before proceeding any further it is necessary to provide a brief outline as to what is meant by metaphysical realism and nominalism, firstly what is metaphysical realism?

Metaphysical realism is the set of beliefs explaining how reality is built up in two layers, particulars and universals. Loux explains metaphysical realism as being the belief “where objects are similar…there is some one thing that they share or have in common”[1], therefore we can think of reality as consisting of concrete objects which occupy a single set of spatial co-ordinates, for sake of example call them Α, Β, Γ, but for the realists there is a second layer to reality, the realm of abstracts. These abstracts are capable of occupying multiple sets of spatial co-ordinates simultaneously. It is in the realm of abstracts similarities between Α, Β, Γ resides in the form of universals, which shall be named Φ.  So long as Α, Β, Γ share a common attribute they share the same relationship with Φ, this relationship allows us to understand how they differ from each other to allow knowledge to become possible.

One philosopher to argue that reality was defined by a set of universals was Plato who proposed that knowledge can only be truly grasped by obtaining an understanding of what he called the Forms. Plato’s theory of the Forms is most famously put forward in The Republic where Plato claims that “for all the sets of particular things which we have regarded as many; and we proceed to posit by contrast a single form”[2], which means that Plato is suggesting that particulars can be grouped by a common characteristic, which takes shape as a Form residing in a realm beyond our sensory perception, A similar view is held by Kant later on when talking about the noumenal.  For Plato the sensory realm, or “the twilight world of change and decay”[3] cannot hold knowledge just doxa (opinion) as particulars are always in a state of flux, a view first proposed by Heraclitus some years before when claiming that “It is impossible to step twice into the same river”[4], thus knowledge of particulars without reference to the universal is nothing more than subjective opinion.

However unlike some realists Plato does not go as far as to say that the universals and particulars exist in entirely separate realms, although upon first sight it may appear this is exactly what Plato implies. In fact Plato proposes that the realm of the Forms and “the twilight world of change and decay”[5]  are actually both joined together as he explains in 476a of The Republic; “That, since beauty and ugliness are opposites, they are two…And as they are two, each of them is single…but they seem to be a multiplicity because they appear everywhere in combination with actions and material bodies”[6], this could be interpreted to mean that even though it may seem that universals and particulars exist separately governing different aspects of understanding they are really co-existing with each other as the universals reside within the particular and the particular can only be indentified so long as the universals exists within it. Hence what we have a monist based realism where universals and particulars are two dimensions to the same object.

On the other hand we have nominalism, according to the Stanford Encyclopaedia of Philosophy “The word ‘Nominalism’…in one sense, its most traditional sense, it implies the rejection of universals. In another…it implies the rejection of abstract ideas.”[7] So it becomes quote clear are nominalists believe that reality only exists of particulars. In the first instance the nominalists would accept that abstract ideas exist, such as numbers and other non-spatiotemporal objects, but only in the sense that they, like all objects, must be particulars. In the second instance the nominalist would accept that universals exist but the only universals are non-spatiotemporal objects whilst everything else is a particular. Either way what is certain is that nominalists claim that real objects can only be concrete particulars, where they differ is what non-spatiotemporal, or non-concrete, objects can be classified as,  therefore “Nominalism, in both cases, is a kind of anti-realism”[8].

In support of the nominalist theory of reality there is Plato’s pupil Aristotle, who in The Metaphysics attempts to prove why the Forms are not a feasible way of looking at reality. One criticism Aristotle makes against the Forms is “But above all one might raise the problem what the Forms…might contribute to the eternal things or to things that come into being and are destroyed…And indeed they do not contribute in any way”[9], the point being made here is the Forms do not actually add anything to the particular they represent not do they add anything to the particulars existence nor take anything from it, therefore the Forms have no value and should not be taken as serious train of thought when describing reality. Aristotle later adds to this criticism “it would seem to be impossible that the substance should exist apart from that of which it is the substance”[10] meaning that the universal could not exist in a realm outside our own as anything that exists does so within the sensory realm in the form of substance. Although as it has already been explained Plato did not claim that there were two separate realms but that they both co-existed as one, thus it could be argued Aristotle misinterpreted Plato’s teachings and therefore misunderstanding Plato’s monist realism.

However by accepting Plato as a monist it does suggest that Plato holds some nominalist leaning, as by claiming that universals and particulars are two dimensions to the same object then they must co-exist within each other. This would mean that there is no such thing as an independent universal entity residing beyond the sensory realm. Therefore if this be the case then it would better to think of universals, in Plato’s monist realism, as abstract ideas from here on as to avoid confusion.

Even though it appears that Aristotle is a nominalist by looking at several other passages in The Metaphysics it is possible to see the outlines of a realist system coming through. In 1006b Aristotle says “all properties are accidents…we can draw the distinction between substance and accident”[11] by properties Aristotle means attributes such as beauty, which Plato argues are Forms, and by substance Aristotle is referring to matter which is the building blocks for particulars but yet is a universal in itself., this can be further supported by Aristotle’s claim that “in the case of things that are, the primary object is substance”[12] which leads on to “everything is connected to the primary”[13], hence everything that exists is substance and substance must be the first cause for everything.


So what actually is substance? To answer this it must first be asked what exists? The answer to which can be found within the teachings of Parmenides who said “It must be what can be spoken and thought is, for it is there for being”[14]. So what exists is anything that can be spoken and thought of, in which case as long as we are able to conceive or universals, be they Forms or the notion of substance, then universals exist. Furthermore as Aristotle argues that substance is the first cause for everything, and substance can be considered a universal then it follows that universals are the first cause for everything, or at least everything concerned with knowledge. Even the Pre-Socratic thinker Anaximander believed that there was such a thing as a first cause, and therefore a universal, as he claimed “the first principle and element of existing things was the boundless”[15], this ‘boundless’ would later become known as substance after Aristotle published The Metaphysics.

Another philosopher writing on this problem is the medieval thinker Boethius, who takes Aristotle’s arguments on genera and species and places them under scrutiny. One way of interpreting what is meant by these two terms is to rename genera as universals, as Aristotle claims that substance is a genera, whilst species are particulars, as all else comes from substance.  Boethius argues that “genera and species cannot exist. This is understood on the following grounds. Everything that is common to several things at one time cannot be one.”[16] By this it is meant that if a universal exists, as is believed, in all particulars resembling it simultaneously, then substance cannot be a single entity but multiple entities because “it cannot happen that although it is a whole in several things at one time…in itself it is one in number.”[17] Boethius later goes on to argue “Now if a genus is one in number, it cannot be common to many. For one thing if it is common, is either common by parts…or…it passes into the use of those who have it”[18], or in other words a single entity cannot wholly exist within a multitude of other existents for this would mean that the former would not be a single entity but a multitude in itself. This is an argument very similar to Aristotle’s which goes “how is one Form to come from many Forms? …if they share the Form, then many absurdities will follow, but if do not, then they will neither be like each other”[19]. This argument is a direct attack against Plato’s theory of the Forms as universals the former part making the point already stated earlier, with the latter part stating that if a single universal does not stand above particulars holding the attributes that create their resemblance then how are we able to distinguish between particulars? Thus if we cannot do this then knowledge falls down as we would have to constantly re-learn what each existent is whenever we come across it, also this being the case any concept of language would become meaningless as we would not be able to exchange views on matters reducing communication down to the wriggling of a little finger.

After looking at both sides of the argument it would seem that truth lies within metaphysical realism, despite the efforts of Boethius and Aristotle who attempted to propose a nominalist doctrine, as without the existence of universals any concept of knowledge and language would become impossible leaving us only with subjective opinion but no way to communicate these opinions between each other to build any truth from them. Even the nominalists acknowledge this difficulty has they claim that universals may not exist but abstract ideas (i.e. substance) do, so that we have a starting point to build upon. Or abstract ideas don’t exist but universals do. Either way the nominalists still end up falling back upon some sense of metaphysical realism, thus leaving the view on shaky foundations. Even if we were to take Plato’s monist idea and say universals and particulars are two dimensions of the same thing then they may eliminate the notion of universals existing independently, however it still leaves open the possibility of abstract ideas which now exist within things. Thus we remain with a metaphysical realism, albeit one with more sympathy towards nominalism.


  • Aristotle, 1998, The Metaphysics, London; Penguin Books
  • Kant. I, 2007, Critique of Pure Reason (Reissued Edition Translated by Smith), Basingstoke (Hampshire); Palgrave Macmillan
  • Loux. M. J, 2007, Metaphysics a Contemporary Introduction (3rd Edition), Abingdon (Oxfordshire): Routledge
  • Plato, 1993, Phaedo, Oxford; Oxford University Press
  • Plato, 2007, The Republic (Revised 2nd Edition), London; Penguin Books
  • Spade. P. V, 1994, Five Texts on the Medieval Problems of Universals, Indianapolis; Hackett
  • Waterfield. R, 2000, The First Philosophers, Oxford; Oxford University Press
  • [accessed 23rd October 2009]

[1] Loux, Metaphysics a Contemporary Introduction (3rd Edition), 2007, Pg. 17

[2] Plato, The Republic (Revised 2nd Edition), 2007, 507b

[3] Plato, The Republic (Revised 2nd Edition), 2007, 508d

[4] Plutarch in Waterfield, The First Philosophers, 2000, Pg. 41

[5] Plato, The Republic (Revised 2nd Edition), 2007, 508d

[6] Plato, The Republic (Revised 2nd Edition), 2007, 476a

[9] Aristotle, The Metaphysics, 1998, 991a

[10] Aristotle. The Metaphysics, 1998, 991b

[11] Aristotle, The Metaphysics, 1998, 1006b

[12] Aristotle, The Metaphysics, 1998, 1003b

[13] Aristotle, The Metaphysics, 1998, 1004a

[14] Simplicius in Waterfield, The First Philosophers, 2000, Pg. 58

[15] Theophrastus in Waterfield, The First Philosophers, 2000, Pg. 14

[16] Boethius in Spade, Five Texts on the Medieval Problems of Universals, 1994, Pg. 21

[17] Boethius in Spade, Five Texts on the Medieval Problems of Universals, 1994, Pg. 22

[18] Boethius in Spade, Five Texts on the Medieval Problems of Universals, 1994, Pg. 22

[19] Aristotle, The Metaphysics, 1998, 991b


Posted on July 2, 2011, in metaphysical, philosophical and tagged , , . Bookmark the permalink. Leave a comment.

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